Ironstone

In the Middle Jurassic, 174 to 161 million years ago, what is now the UK was located roughly where the Mediterranean is now. In a region with a hot climate, weathering of the land surface released iron, which was incorporated into sediments by chemical processes in a shallow sea, forming the ironstone parts of the Northampton Sand Formation.

This band of ironstone extends for about 60 miles, from around Towcester, through Northamptonshire almost to Lincoln. Iron content in the stone is 25 to-30 percent and this example shows the characteristic boxstone structure of concentric banding of harder and softer iron minerals.

Northamptonshire ironstone was used by the Romans and in medieval times, but was then largely forgotten until the 1800s when samples were displayed at the Great Exhibition in 1851.Over the next 125 years, following the development of railways, iron ore was extracted from opencast quarries, and some mines, particularly around Wellingborough, Kettering, Finedon, Corby and Irthlingborough. Extraction methods developed from using picks, barrows and planks to steam, then electric, shovels, and later huge walking draglines. The iron content, around 25-30%, of the Northamptonshire ironstone was increased to around 40 percent by calcining (burning with coal to drive off volatiles, reduce the ore’s weight, and change the ferrous carbonate rock into ferric oxide).

The effect of this major industry on Northamptonshire's landscape was dramatic, but now is almost invisible.

Number 2 of the objects selected for the A History of Northamptonshire in 100 Objects Exhibition 2025